An injection-molding machine provided with such a centering assembly is the subject matter of my commonly owned prior U.S. Pat. No. 4,179,254. More particularly, the injection mold described and shown in that patent has a male portion with a tapering core surrounded by a locking ring; this male portion and a coacting female portion on the other platen serve to produce a cup-shaped workpiece which adheres to the core when the mold opens and is dislodged therefrom by a stripper ring also surrounded by the locking ring. According to a mold structure referred to as prior art in that earlier patent, the assembly of male mold portion and locking ring remains intact when the mold opens while the stripper ring is displaceable relatively to that assembly by actuating rods traversing the base of the core. According to another structure, embodying the invention claimed in that prior patent, the locking ring is separable from the male mold portion in the mold-open position and is coupled with the stripper ring for joint displacement therewith under pressure of an adjacent stripper plate.
U.S. Pat. No. 4,179,254 does not give details on the manner in which the two mold portions are secured to their respective platens. According to conventional practice, the female mold portion is solidly mounted on a backing plate--as by being closely fitted into a depression thereof--while the assembly of male mold portion and locking ring is initially attached to a similar plate with a loose fit, with the aid of hand-tightened screws passing through wider bores in the plate, so as to be laterally shiftable relatively thereto. Upon a preliminary mold closure, which brings about the proper alignment of the male and female portions, the screws are further tightened to immobilize the core and the associated locking ring on its backing plate. This procedure is rather time-consuming and does not prevent subsequent misalignment during operation, e.g. by thermal causes due to unavoidable temperature differences.
This problem is especially serious when the workpieces to be molded are thin-walled cups whose walls would be severely weakened by an offset between the axes of the core and the outer cavity wall. Corrective measures to be taken upon interruption of a production run are especially laborious in a multicavity model requiring individual adjustment of each core and associated locking ring.
Similar problems can arise in die stamping of workpieces such as coins confined in a closed space during the stamping operation.